ide-tape: remove pipeline-specific code from idetape_end_request()

As a side effect, remove unused idetape_kfree_stage() and
idetape_abort_pipeline()

[bart: resurrect taking tape->lock + clearing IDETAPE_FLAG_PIPELINE_ACTIVE]

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>